Topic: Hot Air when ac off
in Forum: C3 Cooling and Heating Systems
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Biloxi, MS - USA
Joined: 8/12/2013
Posts: 4
Vette(s): 1977 Pearl White Coupe
383 Stroker
Does anyone know why I would have hot air coming out of my floor vents anytime my air conditioner is turned off? I got the air blowing cold, now when off, my floor vents seem to blow hot air. Any ideas welcomed. Thanks, Tom
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Lifetime MemberModerator
Duncanville, TX - USA
Joined: 11/8/2003
Posts: 20214
Vette(s): #1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/
Am-Fm/map light National/Regional/Chapter NCRS "Top Flight"
#2-1985 Bright Red/Carmine Cp.L-98/auto
Member: NCRS, NCRS Texas, Corvette Legends of Texas
Yup...."Astro Ventilation"....ain't it GREAT?! The fan shouldn't run if the HVAC system is turned "Off", but it will any other time, to keep air circulating.
Joel Adams
C3VR Lifetime Member #56 
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"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"
Yup! Our C3's seem to produce excessive hot air through the floor vents all the time.
I got so sick of that I installed shut off valves in both heater hoses which I turn off during the warmer months. No direct supply of hot anti-freeze to the heater core helps cool things down in the cabin. It does make a big difference!
Several C3VR members have done this with good results.
Hope this helps.
Kevin
Lifetime MemberManteca, CA - USA
Joined: 11/20/2005
Posts: 3623
Vette(s): 1978,two tone,Metalic Rootbeer & gold
1975 L48 4 speed
Someone on this forum pointed out once that the rubber gasket around the top of the hood (when open) controls a lot of hot air coming off the engine. Evidently, if the gasket isn't working right, hot air from the motor comes from under the hood and goes directly down the vents below the windshield. This member found his own rubbery, spongy material approximately 1 in. square in diameter and replaced the original material, extending it down the sides of the hood further than stock. He claimed it made a significant difference, though I have yet to try it myself, I definitely intend to.
Jimmy B.
Just can't wait to get on the road again. 
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Ellijay, GA - USA
Joined: 1/2/2007
Posts: 38
Vette(s): 1996 Collector Edition Coupe, LT4, 6 spd
1982 Red on Red, 60k miles
1970 Convert, Maroon, Lt Saddle, 383 4 spd conv with ac
2016 Z-51 yellow Convert, 7 speed (Sold)
1974 Avanti w/Chevy 350 - 4L60 trans
2020 Polaris Slingshot GT LE
The 77 had a hot water shut off valve that might not be working. It is turned off when it has vacuum. If the hose is hot behind the valve after it has ran for a while the valve may be defective. Or there is a vacuum valve under the dash behind the RH passenger side of dash that allows the valve to work when the heater control is all the way to cold. That valve may be defective or out of adjustment. It also allow the RH vent to close in the MAX position. If that is not happening the valve under the dash is not working. Lastly you actual heat/Ac control valve may be defective.
All that assumes you have good vacuum going to your control to start with!
All the solutions posted before apply too! So if the valve is working and the vacuum valve under the dash is working and you have the hood sealed you should have somewhat cool air coming in the vents. There are about 10 levels of failure that can cause the problem starting with the fact the corvette has a hot engine in a small engine bay and generates a lot of heat! Good luck!
Gary
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United Kingdom
Joined: 7/15/2015
Posts: 6
Vette(s): 1978 C3 Special Edition Indy Pace Car
New query but really part of the same thread.
1978 Corvette Pace Car. Had aircon which has now been removed, at least some of it. Compressor and condensor in front of radiator and most of the under bonnet (hood) gubbins has gone. I think most of the bits are still in the passenger compartment.
As per other people on this thread I have the problem of too much heat coming into the cabin. Originally the heater wasn't turning off as the control was broken but I have replaced this and this now blows cold air.
I get waves of hot air while driving, but not while stationary. I have extra vents in the footwell which I assume were part of the aircon but as it is not possible to drive with my head and hands in the footwell I can't tell if the hot air is coming through these or just the heat coming through the bulkhead and floor as described elsewhere.
I can see what look like vacuum actuators in the passenger footwell but can't tell if this should be opening/closing a vent, or if it is working.
A few basic questions to start with.
1) If I just block up these vents is this likely to help?
2) Is it likely to cause me any problems?
3) If the actuator in the passenger footwell was part of the aircon which i have no intention of re-installing - is it ok to remove it?
Tony Merrygold, The Open Road
Warwick, England
in Forum: C3 Cooling and Heating Systems
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